The present invention relates to a high-pressure pump with a removable on-off valve for feeding fuel to an internal combustion engine, particularly a vehicle engine.
Various types of high-pressure fuel feed pumps are known, and which are generally supplied with fuel from a normal tank by a low-pressure pump. The high-pressure pump normally comprises an on-off valve, which is opened automatically by the fuel fed to it by the low-pressure pump.
The body of known high-pressure pumps encloses at least a fuel compression chamber, and an actuating chamber housing pump actuating members; and the on-off valve is formed in the pump body, and comprises a shutter designed to ensure fuel flow to the actuating chamber, even when the valve is closed, to lubricate and cool the actuating members.
In one known radial-piston pump in particular, the pump body houses three cylinders, in which slide respective pistons activated by a common cam carried by a shaft activated by the drive shaft; the cam is housed inside the actuating chamber or case of the pump; and the shutter is in the form of a hollow cylinder and slides along the wall of a radial hole in the pump body.
The pump body also has a fuel feed conduit for feeding fuel from the radial hole to the cylinders; the feed conduit is closed by the lateral wall of the shutter; and, to lubricate and cool the pump shaft, the cam, and the various pump body and piston friction surfaces, the shutter also has a calibrated axial hole permitting continuous fuel flow to the case.
To prevent fuel accumulating in an engine cylinder, in the event the respective injector breaks down, or to prevent fuel from being drawn from the actuating chamber in the event supply by the low-pressure pump is cut off, e.g. due to a fault, or in the event an emergency procedure is activated, the shutter is closed automatically by a compression spring when the pressure of the incoming fuel falls below a given value.
The spring rests on a perforated plate normally fixed, e.g. welded, to the opposite end of the guide hole of the shutter.
To ensure the high-pressure pump is also lubricated when fuel flow at the inlet is lowxe2x80x94e.g. when the engine is turned on and the low-pressure pump is activated directly by the internal combustion enginexe2x80x94the on-off valve hole is connected directly to the actuating chamber by an auxiliary conduit.
In this known type of pump, machining the radial hole in the pump body, fixing the plate, and assembling the spring are difficult, high-cost operations involving considerable time and highly skilled personnel. Moreover, the perforated plate at the end of the hole facing the case limits to a certain extent the outside diameter of the cam and, hence, the capacity of the pump under given conditions.
Finally, the feed and auxiliary conduits are each defined by two holes arranged crosswise to each other inside the pump body and formed using a drilling tool from outside the hole; and both the cross holes must be closed at respective ends by forcing respective normally spherical plugs inside the holes.
It is an object of the invention to provide an extremely straightforward, reliable high-pressure pump having an on-off valve which is cheap to produce and easy to assemble, so as to eliminate the aforementioned drawbacks of known pumps with on-off valves.
According to the present invention, there is provided a high-pressure pump with a removable on-off valve for feeding fuel to an internal combustion engine, wherein the pump comprises a body including at least a fuel compression chamber and an actuating chamber enclosing actuating members of said pump, said on-off valve being connected to an inlet conduit of the pump, and is characterized in that said valve is defined by an independent operating assembly insertable in fluidtight manner inside a hole in said body; said hole connecting said inlet conduit to said actuating chamber.